1. Field of the Invention
The present invention relates to water heaters and more particularly to a water heater with an improved water-heater-controller assembly and an improved water-heater-control method.
2. Description of Related Art
Water heaters are used in homes, businesses and just about any establishment having the need to heat water. Water heaters heat water using the simple “heat rises” principle. In operation, water heaters heat cold or ambient temperature water entering at or near the bottom of the water heater to a desired temperature using a gas-fired burner, an electric heater or some other form of energy. During a heating cycle, the cold or ambient temperature water at the bottom of the water heater becomes hotter and begins to rise towards the top of the water heater. Denser water, once on top of the water being heated, falls toward the bottom of the water heater so that it can be heated to the desired temperature. After the temperature of the water at the bottom of the water heater reaches a certain desired temperature, the water heater stops heating the water.
When demand for hot water arises (e.g., someone turns on a faucet to run a shower), fresh, cold or ambient water enters the water heater and “pushes out” or supplies the hotter water at or near the top of the water heater. When a sufficient amount of the hotter water exits from the top of the water heater so that the fresh, cold or ambient water entering the bottom causes the temperature of the water at the bottom of the tank to drop below the desired temperature, the water heater repeats the heat cycling.
A conventional water heater typically has at least one heating element or “heater,” such as a gas-fired and/or electric burner. To take advantage of the “heat-rises” principle, the heater is located at or near the bottom of the water heater. Each water heater typically also has at least one thermostat or controller for controlling the heater.
To facilitate the heating of water, the controller receives signals related to the temperature of the water. When these signals indicate that the water temperature is below a predetermined threshold, for example, when the water temperature is below 120 degrees Fahrenheit, the controller turns on the heater and the water at or near the bottom of the water heater begins to heat. After some time, the temperature of the water at the bottom of the water heater increases to a second threshold, which, for example, may be about 140 degrees Fahrenheit. When receiving signals indicating that the water temperature at the bottom of the tank is greater than the second threshold, the controller causes the heater to reduce its heat output or, alternatively, causes the heater to turn off. The heat cycle begins again when the temperature of the water at the bottom of the water heater drops below the first threshold.
Unfortunately, the signals received by the controller only indicate the temperature of the water close to or at the water heater's bottom. Consequently, the water at the top of the water heater, i.e., the water supplied upon demand, may be at a different temperature from the water at the bottom. The water at the top is typically hotter than or close to the same temperature as the water at the water heater's bottom. Further, depending on demand for water, heat cycling, and heat loss, water temperature throughout the water heater might not equalize. Generally, in operation, the temperature of the water in the water heater does not equalize, but rather has one or more temperature gradients. That is, there may be hot and cold “spots” within the water heater, which can cause problems with outgoing temperature of the water. In some cases, these gradients may become substantial.
In one situation, when the demand for hot water from the water heaters is rapidly cycled on and off, the controller may follow in sequence. Cycling the controller on and off in turn cycles the heater on and off. Consequently, the water within the water heater may become layered by temperature. This phenomenon is known as temperature stacking or stratification. Because of temperature stratification, the temperature of the water at the top of the water heater during this multiple cycling might be within or close to the first and the second threshold. Thus, upon demand, delivered water may be hot or cold. In this situation, as well as others, the water heater may be energy inefficient, since the heater will needlessly cycle on when the water temperature at the top of the water heater is within an acceptable range.
Thus, it is desirable to provide a method and system to better control the delivered water temperature, and to control the temperature of the water in an energy-efficient manner.